The present invention relates to a focus detecting camera, and more particularly, to a focus detecting camera which automatically detects the in-focus condition when a moving object being photographed reaches a position at a preset distance from the camera position.
As is well known, a conventional camera with an automatic focus detector such as a single lens reflex camera with an automatic focus detector is constructed as shown in FIG. 1. Specifically such a camera includes a movable reflex mirror 1, a taking lens 2, a focusing screen 3, a pentagonal prism 4, a total reflection prism 5 and a photoelectric transducer element 6 for focus detection. The movable mirror 1 is normally inclined at 45.degree. to the optical axis for photographing and is raised outside of the optical axis during photographing. Light transmitted through the taking lens 2 is reflected by the movable mirror 1 to reach an eyepiece window of a view finder (not shown) through the focusing screen 3, the pentagonal prism 4 and so on, thereby an object image being observed from the eyepiece window. The central part of the movable mirror 1 forms a semitransparent portion 1a behind which the total reflection mirror 5 is disposed. Light transmitted through the semitransparent portion 1a is reflected downward by the total reflection mirror 5 which is disposed backwardly of the portion 1a to impinge upon the transducer element 6 which is disposed downwardly of the optical path so as not to intercept it and in the position conjugate with a film 7. In such an arrangement of single lens reflex cameras, a properly focused picture of an object may be obtained on the film surface 7 by moving the taking lens 2 back and forth so that the amount of light incident upon the transducer element 6 is maximized.
With the focus detecting camera described above, a focus detection operation is conventionally performed by moving a taking lens back and forth with a motor until an in-focus condition is met. Once the in-focus condition is met, the shutter of the camera is automatically released. Although this procedure is highly satisfactory for taking a picture of a stationary object, it is often unsatisfactory when taking a picture of a moving object since more time is needed to move the taking lens to its focused position and it is difficult for the taking lens to follow a rapidly moving object. Hence, it is practically impossible to obtain a precise focusing, with the result that a desired picture may be missed.
Therefore, when taking a picture of a moving object with a conventional camera of this type, the user normally employed a normal photographing procedure in which the camera switches the camera to its manual operation so as not to move the taking lens by the automatic focusing circuit. Rather, the desired distance of the object is preset manually and the shutter is released manually when the moving object reaches the preset distance. However, this procedure is extremely inaccurate because of the need to make an estimate of the object distance. In addition, it is necessary for the above conventional camera to provide a mechanism for delivering the drive power of a motor and so on to a taking lens. As a result, the camera must be of a larger size and weight. Also, when the procedure is applied to a camera with interchangeable lenses, for example a single lens reflex camera, it is necessary to provide means for delivering the drive power for all interchangeable lenses associated with the camera. This makes the camera system disadvantageously expensive.
The difficulty in operation and the inaccuracy in focusing as described above are common to cameras with a focus detection mechanism consisting of the trigonometrical range finding mechanism. Particularly when taking pictures of wandering children, ecological pictures of moving animals or the like, great skill is required. In the latter case, it is common to use a camera apparatus employing infrared rays that automatically release the camera shutter when animals break through the infrared rays. This requires a large scale infrared ray apparatus and besides it is impossible to take a picture in an accurate in-focus condition because an object distance varies depending upon a position where an animal breaks through the infrared rays.
To overcome many of the foregoing problems, the inventor has already provided a focus detecting camera in which the shutter is automatically released by an automatic focus detection circuit when a moving object reaches a preset distance position. However, this focus detecting camera has a switch for switching between an automatic release and a manual release mode of operation. At the time of automatic release where a shutter is released in response to a focus detection signal, it is necessary to operate the switch. Such switching operation is troublesome and is is easy to forget. As a result, there are frequent occasions when preparation for taking a picture is not completed in time to take a picture of a rapidly moving object and the chance for a desired picture is lost.
With a conventional camera of the electromagnetic release type, a shutter release button is, by way of example, generally constructed as illustrated in FIG. 2. Specifically, a shutter release button 9 is controlled by a stopper (not shown) while biased upwardly by the resilience force of a coiled spring 11 interposed between a flange portion 9a of the shutter release button 9 and a stationary member 10 within a camera body 8. A switch 12 for a normally open electromagnetic release is disposed under the shutter release button 9. Accordingly, when the shutter release button 9 is depressed against the resilience force of the coiled spring 11, the release portion 9b depresses the movable contact piece of the switch 12 to close it. This causes a shutter to be released by placing a release mechanism into operation under activation of a shutter release circuit (not shown). Therefore, assuming that a changeover switch to be operated for an automatic release is provided on the camera, it would be generally arranged independently of the shutter release button 9 without cooperating therewith. When so arranged, operation of the a changeover switch is troublesome. Therefore, if an automatic release as well as a normal release is performed in cooperation with the operation of a shutter release button, the troublesomeness of the operation at the time of the automatic release as described above could be resolved.